The invention relates to a process and device for releasing a signal which indicates that a predetermined load limit value has been reached in the driveline of an agricultural implement which is driven by a tractor, is self-driving or stationary and which comprises a torque limiting coupling whose input and output speeds are measure. The slip revolutions corresponding to the speed differential being added up.
From EP 0 137 247 A2 there is known a device for protecting a coupling against overheating, which device is arranged between an engine and a gearbox. For protecting the coupling against overheating there is provided a device which determines the driving torque which, via the speed determined, permits the slip values to be added up and which total, via a comparison with preset slip values, is used for releasing warning signals.
DE OS 29 10 365 describes a process for releasing an indication in the case of which each tractor implement is associated with a resistance combination characterizing the respective overload protection and determining the nominal values of an overload coupling via an electronic switching assembly.
From U.S. Pat. No. 4,039,781 it is known to arrange a coupling between a drive and an extrusion machine, which coupling, via speed transmitters, records the input and output speeds and which, via an associated switching assembly, permits the control of the coupling and the release of an acoustic warning signal when overloading occurs.
In the engineering field, there are already prior art processes and devices for measuring the torque existing in a driveline and for releasing signals when a predetermined limit value has been exceeded, with the change in torque being used to determine in advance whether a predetermined limit value has been exceeded. The switching process is initiated before the predetermined limit value is reached so that even before the limit value is reached the signal ensures automatic switching off by disconnecting the coupling (DE 34378087 C2.)
Such processes and devices are not suitable for use in connection with agricultural implements, since in agricultural implements it is necessary to permit short-term overloading if it occurs in the course of starting the implement for accelerating the masses to be moved. Furthermore, the device must be suitable for withstanding the rough operational conditions of agricultural implements.